Platelet hyper reactivity has been correlated with coronary events and mortality in patients with coronary artery disease (CAD). An increasing number of studies are finding associations between polymorphisms of platelet adhesion receptors and CAD syndromes, but little information is available suggesting these genetic changes affect platelet function. The applicants preliminary data supports our hypothesis that these polymorphisms promote platelet hyper reactivity and modulate the effects of anti-platelet agents. The goal of this research project is to characterize the effect of genetic variations in platelet adhesive glycoproteins on platelet physiology, focusing on hyper- reactivity, or "gain-of-function" polymorphisms, or mutations. In Aim 1 a large database of platelet functional studies will be generated from three different populations. Unlike standard clinical platelet aggregometry that is designed to measure platelet hypofunction, these assays will assess global platelet hyper-reactivity, reactivity of specific adhesive receptors, and procoagulant effects in collaboration with Dr. Thiagarajan at the University of Texas. DNA and platelet protein and RNA will be prepared from each donor. In Aim 2, samples will be genotyped for candidate markers and rigorous statistical analysis performed to test for associations with the platelet hyper reactive phenotype. The DNA will also be used to test for associations between platelet reactivity and candidate polymorphisms identified by Dr. Berndt in Melbourne and Aim 3 of this proposal. Our previous work characterizing genetic defects in disorders of platelet hypofunction will serve as a model for the studies in Aim 3. Guided by assays that indicate which adhesive receptor is prothrombotic, we will analyze protein, RNA and DNA from patients whose platelets demonstrate an in vitro hyper-reactive phenotype in order to novel polymorphisms or mutations. In Aim 4, candidate polymorphisms or mutations will be tested functionally in cell lines, including their effects on binding to immobilized ligands under shear stress by Dr. Lopez in Houston. These studies would greatly enhance our understanding of genetic effects on platelet physiology, and provide a rationale for tailoring anti-thrombotic therapy according to a patient's thrombotic risk phenotype.